Steam plasma arc hydrolysis of ozone depleting substances

ABSTRACT

A two step process for the destruction of a precursor material using a steam plasma in a three zone reactor wherein the precursor material is hydrolyzed as a first step in the high temperature zone of the reactor, followed by a second step of medium temperature oxidation of the reactant stream in the combustion zone of the reactor where combustion oxygen or air is injected and immediate quenching of the resulting gas stream to avoid the formation of unwanted by-products. A related apparatus includes a non transferred direct current steam plasma torch, an externally cooled three zone steam plasma reactor means for introducing the precursor material into the plasma plume of the plasma torch, means for introducing the combustion air or oxygen into the combustion zone, means for exiting the reactant mixture from the reactor and means for quenching the reactant mixture located at the exit end of the reactor.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.14/269,831, filed May 5, 2014, which is a divisional of U.S. patentapplication Ser. No. 13/424,178, filed on Mar. 19, 2012, and whichissued as U.S. Pat. No. 8,716,546 on May 6, 2014. U.S. patentapplication Ser. No. 13/424,178 claimed priority to U.S. ProvisionalApplication No. 61/454,368, filed on Mar. 18, 2011, and to CanadianApplication No. 2,753,043, filed on Sep. 23, 2011.

U.S. patent application Ser. No. 14/269,831, U.S. patent applicationSer. No. 13/424,178, U.S. Pat. No. 8,716,546, U.S. ProvisionalApplication No. 61/454,368, and Canadian Application No. 2,753,043 areeach incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the depletion of the ozone in theatmosphere and, more particularly, to the destruction of ozone depletingsubstances.

BACKGROUND OF THE INVENTION

The Technology and Economic Assessment Panel (TEAP) of the UnitedNations Environmental Program (UNEP) has reviewed and approved a totalof twelve technologies for the destruction of ozone depleting substances(ODS) [1]. For descriptive purposes, these approved technologies can bebroadly classified as incineration technologies, plasma technologiesincluding arc and radio frequency plasma, and other non-incinerationtechnologies [1]. The most widely used current practice, both by ODSprocessing rate and by the number of processing units, for destructionof ODS is either by incineration or by argon plasma technology [1-2].Both technologies use thermal oxidation as the main mechanism ofdestruction. ODS are fed into refractory lined reactors, which areheated to high temperatures in the order of 1200° C. Incinerators usefossil fuel-fired burners to achieve the necessary high temperatures,whereas argon plasma arc is used in the case of argon plasma technology[2-5].

As ODS are inherently fire inhibitors, extreme process conditions areneeded for their destruction. Incinerators require large quantities offossil fuels to achieve the high temperature necessary for ODSdestruction. Ozone depleting substances are fed into the hightemperature zone of the incinerators in relatively small quantitiesalong with air or oxygen [2-5]. Often these incinerators do not havesecondary combustion chambers and the off gases generated are simplydiluted, before emitting to the atmosphere. Consequently, theseincinerators require large quantities of fossil fuels to destroy smallquantities of ODS, generate large quantities of flue gases containingsignificant amount of Cl₂, F₂, NO_(x), SO_(x), VOC, which are hard toremove from the flue gases [2-5]. Also, incineration processes pose avery high potential of emitting toxic products of incomplete combustion,such as dioxins and furans [6].

Plasma destruction technologies use argon, nitrogen or CO₂ as the plasmaforming medium to transfer energy from an electric arc into highdestruction temperatures [4, 7-10]. These technologies still use thermaloxidation as their main destruction method. Direct current plasmatorches are used to heat the refractory lined reactors to highdestruction temperatures. ODS, air and steam are introduced into thedestruction zone and the ODS are combusted. The primary destructionmechanism in these systems is still thermal oxidation and hence hassimilar problems such as production of Cl₂, F₂ and CF₄, which are hardto remove from the flue gas. In these processes, the presence of excessoxygen and air in the high temperature zone still poses the potentialformation of NO_(x), whereas operating at diminished oxygen levels leadto formation of soot, which is hard to remove. Argon plasma technologyrequires high flow rates of high purity argon, which makes it expensiveto use.

Therefore, there is a need in the art for an improved technology for thedestruction of ozone depleting substances.

SUMMARY OF THE INVENTION

It is therefore an aim of the present invention to provide a novelsystem for destroying ozone depleting substances.

Therefore, in accordance with the present invention, there is provided atwo step process for the destruction of a precursor material using steamplasma in a reactor, wherein the precursor material is hydrolyzed as afirst step in a high temperature zone of the reactor, followed by asecond step of medium temperature oxidation of the reactant stream in acombustion zone of the reactor where combustion oxygen or air isinjected and immediate quenching of the resulting gas stream to avoidthe formation of unwanted by-products.

Also in accordance with the present invention, there is provided anapparatus for carrying out the above process, including a nontransferred direct current steam plasma torch, an externally cooledthree zone steam plasma reactor including a corrosive resistantrefractory lining, means for attaching the plasma torch to the reactor,means for introducing the precursor material in the form of gas vortexor fine liquid spray or solid particles into the plasma plume of theplasma torch, means for introducing the combustion air or oxygen intothe combustion zone of the reactor, means for exiting the reactantmixture from the reactor and means for quenching the reactant mixturelocated at the exit end of the reactor.

Further in accordance with the present invention, there is provided anapparatus for the destruction of a precursor material, comprising areactor including a high temperature zone and a combustion zone, thehigh temperature zone being adapted for hydrolyzing the precursormaterial, the combustion zone being adapted to effect medium temperatureoxidation of the reactant stream where combustion oxygen or air isinjected, and a quenching means is provided at an exit end of thereactor for quenching of the resulting gas stream to avoid the formationof unwanted by-products.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of embodiments thereof, given by way of example only withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, showing by wayof illustration an illustrative embodiment of the present invention, andin which:

FIG. 1a is a schematic representation of a complete system fordestroying ozone depleting substances in accordance with one embodimentof the present invention;

FIG. 1b is a schematic representation of a complete system fordestroying ozone depleting substances in accordance with anotherembodiment of the present invention; and

FIG. 2 is a vertical cross-sectional view of a destruction section ofthe present system for destroying ozone depleting substances.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

The present invention uses a steam plasma hydrolysis system S for thedestruction of ODS. The main mechanism of destruction in this inventionis the plasma steam hydrolysis. In this system, a custom designed steamplasma torch is used as the sole source of energy to heat the refractorylined primary reaction chamber to temperatures close to 1500° C.Superheated steam formed from regular water is used as the main plasmaforming gas, along with a small quantity of inert gas. Highly reactivesteam plasma, i.e. hydrogen and hydroxyl ions present in the steamplasma, are used to convert the ODS into CO, HCl and HF, in an oxygenstarved environment. The produced CO is combusted downstream in theprocess followed by an instantaneous water quench. Oxygen starvedenvironment eliminates the formation of toxic substances such as Cl₂, F₂and CF₄ and a rapid quench eliminates the formation of dioxins andfurans. The acid gases formed in the process can either (i) beneutralized with an alkali or (ii) first scrubbed with water to recovera weak acid mixture and then neutralized for the unrecoverable portionof the acid gases. In both cases, a cleaned effluent gas streamcomprising mainly CO₂ is emitted to the atmosphere.

Now turning to the figures of the appended drawings, the present steamplasma hydrolysis system S will be described in more details.

A precursor material 1 is injected, either in the form of a gas vortexor a fine spray of liquid or a stream of solids, into the system S asshown in FIG. 2. The precursor material 1, to be destroyed, is fedadjacent to a plasma torch 4 via a specially designed flange 12. Thisflange 12 is water cooled, made of acid resisting material and isspecially designed to facilitate intimate mixing of the fed precursormaterial 1 with the high temperature viscous steam plasma plume.

An outside heating source, typically a steam plasma torch 4, is used asthe source for heating the refractory lined reactor to a temperature of1500° C. The plasma torch 4 is designed and built with features, toavoid condensation of the superheated steam inside the torch beforereaching the plasma arc. These features of the plasma torch include, (i)direct injection 3 of the main plasma forming gas, superheated steam, tothe torch vortex so that it does not condense on its way to the arcplume and minimizing superheated steam passage inside the torch body;(ii) cooling of the plasma torch body with a hot fluid (propyleneglycol-water mixture), circulating in a high pressure closed loop, toavoid superheated steam condensation; and (iii) use of high temperatureresistant polymers such as Vespel™ or PEEK for torch internalcomponents.

The steam plasma torch 4 includes a metallic cathode 2, a metallicignition anode 6 and a metallic working anode 8, which are arranged asshown in FIG. 2. A plasma arc is initiated with helium or anothermonoatomic gas between the cathode 2 and the ignition anode 6. Once thearc is stabilized 10, a plasma forming steam is injected at 3 and thearc is transferred from the ignition anode 6 to the working anode 8.Nitrogen, helium, argon or mixture thereof is used as a shroud gas 5.The shroud gas 5 protects the metallic cathode 2 from prematureoxidation and hence increases the working life of the cathode 2.Superheated steam is used as the main plasma forming gas 3.

The steam plasma torch 4, in-addition to acting as a heat source,provides reactive oxygen, hydroxyl and hydrogen ions necessary for thedestruction of the precursor material 1 and prevents the formation ofundesired side products, such as Cl₂, F₂, CF_(x). The overall reactioncan be summarized as:CH_(x)Cl_(y)F_(z) +aH₂O→zHF+yHCl+aCO+bH₂ +cH₂O

A refractory lined reactor 14 is used to destroy the precursor material1. A corrosion resistant high durable refractory lining 16 is used asthe working refractory in the reactor 14. For example, a high aluminarefractory (>98% alumina content), such as Kricon 34™ or similar whichis known to resist to corrosive HF and HCl gases, is used as the workingrefractory.

The internal walls of the reactor 14 are coated with acid resistant hightemperature metallic coating such as Hastealloy™ or similar. Theexternal walls of the reactor 14 are cooled externally, either by air orby water, for safety reasons and to limit heating of the furnace room.

The refractory lined reactor 14 comprises of three zones, as shown inFIG. 2. These three zones are:

1) a conical converging, high temperature, steam hydrolysis zone 11,wherein the fed precursor material 1 undergoes steam hydrolysis;

2) a narrow tubular zone 13, which creates high temperature turbulentmixing of the gases and facilitates completion of the hydrolysisreaction; and

3) a conical diverging, medium temperature, combustion zone 15, whereinthe gases are combusted with the combustion air or oxygen.

Combustion air or oxygen 9 is added to the reactor 14, as also shown inFIG. 2. The combustion air or oxygen 9 is metered to the reactor 14 tocontrol the temperature in the low temperature zone of the reactor 14while achieving complete combustion and eliminating the formation ofundesirable by-products such as Cl₂.

A water quench unit 20 is attached right at the outlet of the combustionzone 15 of the reactor 14, as seen in FIG. 2. A set of spray nozzles 18create a fine spray of water 17 in the quench unit 20, which spray ofwater 17 instantaneously cools the gases. This instantaneous quenchingof the gases will prevent the reformation of dioxins and furans. Thequench unit 20 is built as a double-walled water-cooled pipe sectionwith acid resisting material.

A scrubber tank 22 is attached at the bottom of the quench unit 20, asbest shown in FIG. 2. The scrubber tank 22 uses acid resistant plasticsealing material on all sealing surfaces. The internal walls of thescrubber tank 22 are lined with an acid resistant Teflon™-based coatingsuch as Halar® CCTFE, or similar. The scrubber tank 22 acts as areservoir for collecting the quench water 19 and provides the necessarywater head for a scrubber water recirculation pump 28 (see FIG. 1a ).

A standard flue gas cleaning technology, i.e. either a wet off-gascleaning technology using an acid gas neutralizing scrubber 24 (as shownin FIG. 1a ) or a dry gas cleaning technology, is used to remove acidgases from the flue gas.

An induced draft fan 26 draws the off gases through the system S andcreates a slightly negative pressure in the system S, as shown inFIG. 1. The entire system S is maintained under a slight negativepressure (couple of inches of H₂O column) to prevent any escape of acidgases from the system S. At the outlet of the ID fan, the off-gases areexhausted to a stack 23.

In operation, the steam plasma torch 4 heats the reactor 14 to thedesired operating conditions and the precursor material 1 is injectedinto the plasma plume. The highly reactive hydrogen and hydroxyl ionspresent in the steam plasma hydrolyze the precursor material 1 in thehigh temperature hydrolysis zone 11. Additional steam 7 is added to thehydrolysis zone 11. The reacted stream flows through the narrow tubularzone 13, which provides the necessary turbulence and residence time forreaction to reach the combustion zone 15 of the reactor 14. Thecombustion air or oxygen 9 is added to the reactor 14 and the off gasesexiting the reactor 14 enter the water quench 20 located at the exit ofthe combustion zone 15. The off gases are rapidly quenched by the finespray of water 17 created by the spray nozzles 18. The liquid streamsettles in the scrubber tank 22, whereas the off gases exit the scrubbertank 22 and pass through a standard off gas cleaning technology. Eitherwet scrubbing technology or dry scrubbing technology is used to cleanthe off gases from acid gases such as HF and HCl and to convert them toinnocuous salts. The induced draft fan 26 is used to drive the off gasesthrough the system S and create a slightly negative pressure in thesystem S.

Caustic soda or another alkali from a tank or drum 25 is fed to thescrubber water recirculation line 31 by a dosing pump 30 to continuallyadjust the pH of the scrubber solution, neutralizing any acid components(HCl, HF) from the off gases. Neutralized water 21 is removed from thescrubber tank by a blow down line 32.

Now turning to FIG. 1b , a variant steam plasma hydrolysis system S′ isdescribed and which includes a gas cleaning option (ii) whereby a weakacid is produced followed by neutralization of the acid gases

The gases leaving the quench unit 20 are sent to an acid recovery tank22 b, wherein diluted acid is used to scrub the acid gases leaving thequench unit 20. The acid recovery tank 22 b is attached directly at thebottom of the quench unit 20, as best shown in FIG. 2. The acid recoverytank 22 b uses acid resistant plastic sealing material on all sealingsurfaces. The acid recovery tank 22 b acts as a reservoir for collectingthe quench water 19 and provides the necessary liquid head for arecirculation pump 41 (FIG. 1b ). Fresh water 42 is added eithercontinuously or in an on/off mode to the acid recovery tank 22 b inorder to control the acid concentration.

The gases travel counter current to the flow of scrubbing liquid in apacked acid scrubber unit 43. The acid gases get scrubbed as they travelthrough the acid scrubbing unit 43. Weak acid mixture, stream 44, whichgets collected at the bottom of the acid recovery tank 22 b is removedperiodically from the acid scrubbing tank unit 22.

The scrubbed gas stream, stream 45, leaving the acid scrubbing unit 43enters a gas cleaning scrubber unit 46. A scrubber tank unit 47 isattached at the bottom of the gas cleaning scrubber unit 46. Thescrubber tank unit 47 uses acid resistant plastic sealing material onall sealing surfaces. The scrubber tank unit 47 acts as a reservoir forcollecting the scrubbing water and provides the necessary water head fora scrubber water recirculation pump 48.

Caustic soda or another alkali from a tank or drum 52 is fed to ascrubber water recirculation line 54 by a dosing pump 51 to continuallyadjust the pH of the scrubber solution, neutralizing any acid components(HCl, HF) from the off gases. Neutralized water 49 is removed from thegas cleaning scrubber tank by a blow down line 53.

A standard flue gas cleaning technology, i.e. either a wet off-gascleaning technology using the neutralizing scrubber 46 (as shown in FIG.1b ) or a dry gas cleaning technology, is used to clean the flue gas.

Although the present invention has been described hereinabove by way ofembodiments thereof, it may be modified, without departing from thenature and teachings of the subject invention as described herein.

REFERENCES

-   1. UNEP (2002), http://www.ozone.unep.org/teap/Reports/Other Task    Force/TEAP02V3b.pdf-   2. Hai Yu, Kennedy E. M., Adesina A. A. and Dlugogorski B. Z., A    review of CFC and halon treatment technologies—The nature and role    of catalysts, Catalysis Surveys from Asia, Vol. 10, No. 1, March    2006-   3. Hug et. al., Reactor for thermal cracking of hydrocarbons, U.S.    Pat. No. 4,751,076, 1988-   4. Bereczky et. al., Method for treatment of hazardous fluid organic    waste materials, US Patent 2003/0171635 A1, 2003-   5. UNEP (2000)    http://www.unep.fr/ozonaction/information/mmcfiles/3521-e-file1.pdf-   6. Hassel G. R., Experimental Investigation of PIC Formation in CFC    Incineration, Energy and Environ (Res. Corp, Irvine, Calif., USA,    1991)-   7. Deam et. al., Material Processing, U.S. Pat. No. 5,866,753, 1999-   8. Ramakrishnan et. al., Electric arc reactor having upstream and    downstream electrodes, U.S. Pat. No. 5,296,672, 1994-   9. Doolette et. al., Electric arc generating device having three    electrodes, U.S. Pat. No. 5,227,603, 1993-   10. Shimeiwa et. al., Plasma arc decomposition method for    chlorofluorocarbon equivalent material used as coolant, involves    oxidizing carbon monoxide or carbon atoms generated during    decomposition of carbon dioxide by oxidizing gas, Japan Patent    2000334294-A, 1999

The invention claimed is:
 1. An apparatus for carrying out a two stepprocess for the destruction of a precursor material using a reactor,wherein the precursor material is hydrolyzed as a first step in a hightemperature zone of the reactor, followed by a second step of mediumtemperature oxidation of the reactant stream in a combustion zone of thereactor where combustion oxygen or air is injected and immediatequenching of the resulting gas stream to avoid the formation of unwantedby-products, the apparatus comprising: the reactor having three zones,means for introducing the precursor material in the form of gas vortexor fine liquid spray or solid particles into the reactor, means forintroducing the combustion air or oxygen into a combustion zone of thereactor, means for exiting the reactant mixture from the reactor andmeans for quenching the reactant mixture located at the exit end of thereactor.
 2. An apparatus according to claim 1, wherein a non-transferreddirect current steam plasma torch is provided, the plasma torchincluding a setup of metallic electrodes namely cathode, ignition anodeand working anode arranged in a spaced relationship such that a directcurrent electric arc exists between the cathode and the working anodeand uses an inert gas, such as helium, nitrogen, argon or a mixturethereof, as the shroud gas and uses steam as the main plasma forming gasand has a plasma plume exiting at the anode end.
 3. An apparatusaccording to claim 1, wherein the means for quenching is located at theexit end of the reactor, and produces a spray of cold water throughwhich the process stream exiting the reactor passes.
 4. An apparatus forthe destruction of a precursor material, comprising a reactor includinga temperature zone and a combustion zone, the temperature zone beingadapted for hydrolyzing the precursor material, the combustion zonebeing adapted to effect medium temperature oxidation of the reactantstream where combustion oxygen or air is injected, and a quenchingdevice is provided at an exit end of the reactor for quenching of theresulting gas stream.
 5. An apparatus according to claim 4, wherein thetemperature zone of the reactor includes a conical converging, hightemperature, steam hydrolysis zone which provides a necessary residencetime for the hydrolysis of the precursor material, wherein a tubularzone is provided between the temperature zone and the combustion zonefor providing turbulence and additional residence time for thereactions, and wherein the combustion zone of the reactor includes aconical diverging, medium temperature, combustion zone which provides aresidence time for the combustion of the process stream.
 6. An apparatusaccording to claim 4, wherein there are provided a non transferreddirect current steam plasma torch, means for attaching the plasma torchto the reactor, means for introducing the precursor material in the formof gas vortex or fine liquid spray or solid particles into the plasmaplume of the plasma torch, means for introducing the combustion air oroxygen into the combustion zone of the reactor, means for exiting thereactant mixture from the reactor and means for quenching the reactantmixture located at the exit end of the reactor.
 7. An apparatusaccording to claim 6, wherein the three zone steam plasma reactor isexternally cooled and includes a corrosive resistant refractory lining.8. An apparatus according to claim 4, wherein the plasma torch includesa setup of metallic electrodes namely cathode, ignition anode andworking anode arranged in a spaced relationship such that a directcurrent electric arc exists between the cathode and the working anodeand uses an inert gas, such as helium, nitrogen, argon or a mixturethereof, as the shroud gas and uses steam as the main plasma forming gasand has a plasma plume exiting at the anode end.
 9. An apparatusaccording to claim 4, wherein the quenching means produces a spray ofcold water through which the process stream exiting the reactor passes.